Hello Katja QS 

Welcome to the Community page, 

I can help you send batch invoices. Here's how:

1. Go to Sales.
2. In the Invoices tab, select the invoices.
3. Click on status, select either unpaid or paid 
4. Tick the box next to date to select all or tick the boxes you need to send invoices for 
5. Click on Batch actions.
6. Select Send. 
7. Enter the customer email address.
8. Click on Send.